The present disclosure generally relates to compressors, such as those used in turbochargers for internal combustion engines. The disclosure more particularly relates to compressors having a ported shroud and a bypass passage connected to the port in the shroud and to the compressor inlet duct, whereby fluid can flow in either direction through the bypass passage, depending on operating condition, to help alleviate surge and increase flow at choke and thereby extend the usable flow range of the compressor.
In many automotive turbocharger applications, it is a challenging task to supply a compressor having an adequately wide flow range from surge on the low end to choke on the high end. Many workers in this field have developed a host of designs and methods for extending the usable flow range. Probably the most widely used and effective design for compressor flow range enhancement is the ported shroud. In a compressor having a ported shroud in its simplest form, the shroud has one or more ports that extend through it into a bypass passage defined in the compressor housing, and the bypass passage has an end that is fluidly coupled to the inlet duct of the compressor. At low-flow operating conditions near the surge line, part of the fluid that has already been at least partially compressed by the compressor can pass through the port(s) in the shroud and be recirculated back to the compressor inlet via the bypass passage. This has been found to help alleviate surge and therefore allow the compressor to operate down to lower flow rates before surge occurs at a given pressure ratio. At high-flow operating conditions near choke, some of the fluid entering the inlet duct can flow from the inlet duct into the bypass passage and out through the port(s). This has been found to enable a higher flow rate to be achieved.
While this simple ported shroud design is an improvement over non-ported designs, it has been recognized that the optimum port configuration for near-surge conditions is not necessarily (and indeed not usually) optimum for near-choke conditions. Accordingly, some workers in the field have developed variable-geometry mechanisms that enable the port configuration to be varied depending on operating condition.
At least from the standpoint of flow range enhancement, some of these variable-geometry ported shroud designs are improvements relative to fixed-geometry ported shroud designs. However, further improvement is desired.